Fossil fuel based power plants emit carbon dioxide, which is a greenhouse gas. Exhaust gases include up to about 15 percent by volume carbon dioxide, which is required to be isolated from the other gaseous components to reduce the exhaust of greenhouse gases. Other gaseous components may include nitrogen, oxygen and water vapor.
A currently practiced method to capture carbon dioxide involves chemical absorption in an amine solution. When gaseous components are bubbled through an amine solution, the acidic carbon dioxide alone is absorbed by the alkaline amine solution. Later, the absorbed carbon dioxide is released by a thermal process. This process is environmentally unfriendly, costly and requires a large area.
Conventionally, polymeric membranes have been used in gas separation. Thin polymeric membranes lead to a high flux of gas at low pressures. However, the strength of polymeric membranes limits the usable gas pressures and thereby, the flux through the membranes. Also, polymeric membranes may not hold up to the harsh environment and high temperatures of exhaust gas from power plants.
EP Publication No. 0254556 discloses a semipermeable thin film membrane of siloxane oligomers or copolymers for acid gas separation from hydrocarbon gases. The membrane may be formed on a microporous polymer support. As a material, siloxane has the advantage of high permeability to gas molecules and a good selectivity. However, the mechanical properties of siloxane are too poor to impart structural stability.
What is needed is a highly stable membrane for separating carbon dioxide from mixed gases at high flux, at high temperatures and in a harsh environment.